The lanes on roads and highways are normally separated by 10 cm wide painted lines. Typically, the lanes are made visible at night by dropping glass bead onto the wet paint, to make the lines reflective. This method, however, has a number of drawbacks. Firstly, the glass bead used is usually not of a high quality, thus giving a low initial reflectivity. Secondly, the beads tend to be subject to wear by vehicle tires and abrasion from grit on the road. Thirdly, the beads are positioned against the road surface, and are thus covered with water during rain. The film of water interferes with the reflectivity, and makes the line difficult to see at night.
Wet night visibility is greatly enhanced by the addition of reflective raised pavement markers. These raised markers are constituted essentially by a block of durable plastic into which a cube-cornered reflector is imbedded. These markers are cemented to the road along the painted line, and pick up and reflect the light of the approaching vehicle. Such markers have the following advantages. Firstly, the reflector is moulded from durable plastic allowing the quality to be controlled, therefore producing a consistently high brightness reflector. Secondly, the reflector is mounted in the body of the marker in such a way that the reflector is protected to some degree from tire wear and abrasion. Thirdly, the reflector is mounted above the surface of the road and is not covered with water during rainy weather. It therefore performs well in rain.
Such raised pavement markers are very effective and are widely used where climatic conditions are such that snowplowing is unnecessary. Generally, these raised markers cannot withstand the impact of a snowplow.
Many attempts have been made to produce a raised marker that will survive impact from snowplows. There are two basic ways to accomplish this.
The first method is to make a marker that is strong enough to withstand the impact of a snowplow. The most successful product uses this method. The unit is a cast steel insert that is inlaid into the road and retained using epoxy. When in position, the casting exhibits two parallel steel ramps protruding up from the road surface. A reflector is cemented between the ramps for protection. When impacted by the snowplow, the casting deflects the blade upwardly far enough that the blade does not make contact with the reflector. Although these units are widely used, they do have a number of problems due to the extreme impact. Firstly, although the ramp height of the marker may be as little as 1/4" in 6", the plow blade will jump more than 6" off the road, leaving a strip of road unplowed. Secondly, the shock of impact is considerable, and is very uncomfortable for the plow driver. It also has a detrimental effect on the mechanicals of the truck. Thirdly, the impact between the carbide blade of the plow and the casting often results in cracked blades. Fourthly, the casting of the marker is heavy. If it is not installed perfectly, there is a risk that the plow blade will catch on the casting and pull it out of the road. If this happens at high speeds, the casting can become a projectile which can endanger oncoming vehicles and their occupants.
The second method is to make a marker that deflects out of the way on impact with the plow blade without damaging the marker, thus overcoming the problems encountered with the cast unit.
The Prior Art
Several previous patents utilize the deflection principle in order to avoid damage both to the reflector and the plow blade.
U.S. Pat. No. 3,901,614, Overacker, issued Aug. 26, 1975, discloses a reflector unit having a hard transparent material in the upper part of the body and a flexible transparent material forming the base. The base is locked into a hole or recess in the roadway utilizing a suitable compound. The construction is such that the flexible material of the base allows the hard material of the upper portion to move downwardly somewhat under the force of an impact.
U.S. Pat. No. 4,504,169, Jones, issued Mar. 12, 1985, provides a road stud which is displaced downwardly when run over by a vehicle. When this occurs, special flaps are also displaced downwardly, which causes the reflection elements to be wiped by resilient wiping lips to remove dirt.
U.S. Pat. No. 4,597,691, Clarke, issued Jul. 1, 1986, discloses a resilient structure in which a light-reflective surface is depressed to a level coincident with or below the surrounding pavement. Once the force is removed, the light reflecting surface returns to an elevation above the road surface.
U.S. Pat. No. 5,069,577, Murphy, issued Dec. 3, 1991, discloses a unitary flexible pavement marker which is hollow and formed in such away that the upward dome is depressed or "folded" downwardly into the cavity provided below it, upon impact by a tire or a snowplow blade. When the tire or blade have passed by, the marker returns to its original position.
The foregoing prior art approaches to the design of a marker capable of deflecting out of the way on impact retain certain disadvantages which it is an aspect of this invention to overcome.
The Overacker U.S. Pat. No. 3,901,614 requires the provision of a spherical component with a hard top section and a resilient bottom section, both having a particular index of refraction, and both remaining optically transparent. It is obvious that repeated abrasion from impact would eventually ruin the optics of the various portions of the component and interfere with its light-reflecting capability.
The U.S. Pat. No. 4,504,169, Jones, is directed to a unit that has been tested in Ontario with discouraging results. The part of the unit which sits above the road and is subject to contact with a snowplow blade is made of an elastomeric plastic which is relatively soft and tends to be cut by the jagged edge of the blade. The body of the unit is not sealed, and thus allows water and dirt to enter into the unit. The water freezes and this causes the unit to seize so that it will not depress, thus resulting in failure. The general shape of the unit, which was designed to include a method of cleaning the front of the reflectors when depressed, is such that it is subject to be being snagged by the snowplow blade.
U.S. Pat. No. 4,597,691, Clarke, uses only a single dome. The sealing of the unit is accomplished by mechanically compressing gaskets, however these sealing surfaces are subject to leaking and failure. According to the patent, the housing is hollow with an upper open end and a closed lower end. The design of the unit tends to be quite complex, utilizing many parts and mechanical fasteners. This results in increased costs, and greater likelihood of failure.
U.S. Pat. No. 5,069,577, Murphy, is directed to a configuration which was tested in Ontario and failed. It is believed that the main reason for failure is that the soft plastic material protruding above the road surface, when struck by the plow blade, tended to be pinched rather than deflected downward, and the pinching action compressed the trapped air to a pressure which ruptured the back side of the dome.